As is well known, hybrid electric vehicles use an internal combustion engine and a battery together as a power supply. That is, the hybrid electric vehicles efficiently combine power of the internal combustion engine and power of a driving motor.
As illustrated in FIG. 1, a hybrid electric vehicle may include, for example, an engine 10, a driving motor 20, an engine clutch 30 for splitting power between the engine 10 and the driving motor 20, a transmission 40, a differential gear 50, a battery 60, an integrated starter-generator 70 for starting the engine 10 or generating electricity by rotational force of the engine 10, and vehicle wheels 80.
Here, although the integrated starter-generator 70 serves as both the starter motor and the electric generator, the above described integrated starter-generator is related with the starting of the engine, so that the integrated starter-generator 70 is considered as the starter motor.
The hybrid electric vehicle may further include a hybrid controller (HC) 200 for controlling the entire operation of the hybrid electric vehicle, an engine control unit (ECU) 110 for controlling an operation of the engine 10, a motor controller (MC) 120 for controlling an operation of the driving motor 20, a transmission control unit (TCU) 140 for controlling an operation of the transmission 40, and a battery controller (BC) 160 for controlling and managing the battery 60.
The battery controller 160 may be called a battery management system (BMS). The integrated starter-generator 70 may be called an integrated starter & generator (ISG) or a hybrid starter & generator (HSG).
The hybrid electric vehicle may drive in an electric vehicle (EV) mode, which is a true electric vehicle mode only using power of the driving motor 20, a hybrid electric vehicle (HEV) mode, which uses rotational force of the engine 10 as a main power and rotational force of the driving motor 20 as an auxiliary power, and a regenerative braking (RB) mode for collecting braking and inertial energy during driving by braking or inertia of the vehicle through electric generation of the driving motor 20 to charge the battery 60.
The hybrid electric vehicle may start the engine 10 by using the driving motor 20 providing driving force when the starter motor has a failure. For example, in the related art, when the starter motor has the failure, the engine may start by connecting the engine clutch or with the driving force of the driving motor while connecting the engine clutch.
However, according to the related art, the connection of the engine clutch or a difference in torque between the engine and the driving motor generates shock when a fuel injection starts without starting the engine, thus deteriorating driving performance.
That is, according to the related art, in a case where the vehicle is not in a rapid acceleration situation as illustrated in FIG. 2, the shock is rarely generated during the connection of the engine clutch. However, when the vehicle accelerates rapidly such that the driving motor outputs the maximum torque as illustrated in FIG. 3, load compensation for a slip joint of the engine clutch is necessary, thus decreasing acceleration torque and deteriorating acceleration linearity.
In the related art illustrated in FIG. 3, an inclination change of three steps including step 1 which is before the engine clutch for starting the engine is connected, step 2 in which the engine clutch is being connected, and step 3 which is after the engine clutch is connected, is generated, thus deteriorating acceleration linearity.
That is, as described in FIG. 3, the load compensation of the engine clutch is impossible when pressure of the engine clutch is applied, thus generating an abrupt vehicle stop sensation.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure, and therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.